SKY74038 Datasheet, PDF (3/12 Pages) Skyworks Solutions Inc. – 2.6 GHz/800 MHz Dual Fractional-N/lnteger-N Frequency Synthesizer

DATA SHEET • SKY74038 FREQUENCY SYNTHESIZER
DAT
CLK
LE
tDSU
tDHD
tCKL
tCKH
tCLE
Figure 3. SKY74038 Serial Data Input Timing Diagram (MSB First)
tLEC
tLEW
C1457
MSB
LSB
D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
R2 DIVIDER
N2 DIVIDER
LD
SC2
00
IF
EN
SP2 1 0
ME
N1 DIVIDER
R1 DIVIDER PS
FN
SC1 SP1 0 1
RF
11
C1456
Figure 4. SKY74038 Serial Data Word Format
Registers
The SKY74038 includes four 22-bit registers that can be
programmed independently in any order. Bits D0 and D1
represent the register addresses. For more information on
registers, addresses, and format, refer to the Synthesizer Register
Programming section of this document.
A dithering disable function is accessible via word 00, data bits
21 and 20. When the RF synthesizer is programmed for fractional
divide values, bits [21:20] should be programmed to 10b to
enable dithering. However, when the RF synthesizer is
programmed to output a frequency that is a whole integer
multiple of the comparison frequency, the synthesizer should be
programmed to disable dithering (bits [21:20] = 11b). This
improves the phase noise when operating on integer-N
boundaries. These data bits must be programmed after power-up;
otherwise, erroneous device operation may occur. Refer to the
Synthesizer Register Programming section of this document for
bit definitions.
Voltage Controlled Oscillator (VCO) Prescalers
The VCO prescalers, P/P+1 and Q/Q+1, provide low noise signal
conditioning of the VCO signals. They translate from an off-chip,
single-ended or differential signal to an on-chip differential signal.
By changing the PS bit, the RF synthesizer has the option to use
either the 8/9 or the 16/17 prescaler depending on the desired
operational frequency. The maximum frequency is 2.6 GHz for the
16/17 prescaler and 1.4 GHz for the 8/9 prescaler. The IF
synthesizer has a fixed 16/17 prescaler with a maximum
frequency of 800 MHz.
RF and IF Dividers
The SKY74038 provides programmable dividers that control the
prescaler and supply the divided VCO signals to the charge pump
phase detectors. Programmable ratios on the RF fractional-N
synthesizer ranging from 256 to 2¹² are possible with the 16/17
prescaler, and from 64 to 2¹¹ with the 8/9 prescaler. The IF
integer-N synthesizer has a programmable divide ratio ranging
from 256 to 2¹⁷.
Reference Frequency Dividers
The reference signal can be divided by a ratio of 1 to 7 for the RF
reference divider (R1) and from 1 to 8192 for the IF reference
divider (R2). The input frequency for the reference signal can be
as high as 50 MHz.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
101075M • Skyworks Proprietary and Confidential information • Products and Product Information are Subject to Change Without Notice • June 4, 2007
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